The present invention relates to the method of protecting dogs against disease caused by canine parvovirus (CPV). More particularly, it relates to a method of immunizing dogs against CPV by using an alien infectious material from one animal species for the protection against natural disease in a different animal species. The vaccine that is the subject of this invention is a modified live (attenuated) or chemically inactivated feline panleukopenia virus vaccine.
Parvoviruses are characterized as a small animal DNA virus, consisting of an isometric protein capsid and a short molecule of single-stranded DNA. Until recently, there had been no definite isolation and laboratory propagation of a canine parvovirus, although parvoviruses have been recovered and isolated from various animal species (Siegl, The Parvoviruses, Springer-Verlag, New York, 1976). Bachmann et al. include the dog as a possible parvovirus host in a report detailing the characteristics of parvovirus in general (Bachmann et al., Intervirology 10: in press, 1978). In 1970, Binn et al. reported the recovery and characterization of a "minute virus of canines" (MVC) (Binn et al., Infect. Immunity 1: 503, 1970). The isolates described were of canine origin, however, their pathogenicity was not known, and cytopathic effect (CPE) was produced in only a very narrow host range, i.e., only in a single continuous canine cell line, and not in primary canine nor primary or continuous cell cultures from other species. No immunological testing was done. Present data suggest that the Binn isolate is distinct from the pathogenic canine parovirus which is the subject of this application. In 1977, Eugster and Nairn reported a circumstantially-suggested causative link between diarrhea in puppies and a canine parvovirus (Eugster and Nairn, Southwestern Veterinarian 30: 59, 1977). Consistent with Binn et al., above, the isolate reported therein could not be grown in more than a single cell line. Again, pathogenic potential was unexamined and no animal inoculations were performed. In 1978, an apparently new serious enteric disease in canines appeared and became widespread. It is characterized by diarrhea, fever, and diminished white blood cell counts.
The object of this invention is to provide a heterotypic feline viral vaccine for the protection of dogs against disease caused by pathogenic canine parvoviruses. While attempting to develop a homotypic vaccine against canine parvoviruses it was discovered that both living and inactivated commercial feline vaccines, when administered to dogs, provided protection against disease caused by CPV. The cross-relation between the feline panleukopenia virus (FPV) and the canine parvovirus (CPV) is a surprising result since such cross-relations are unusual among the various parvoviruses from different animal host species, e.g., swine-canine, bovine-swine, swine-feline, etc. (Siegl, G., "The Parvoviruses," Virology Monographs 15: Springer-Verlag, New York, 1976). The discovery of this immunological cross-relation represents a distinct advance in the art.
One group of dogs was vaccinated with a commercial modified living (attenuated) feline panleukopenia viral (FPLV) vaccine (Vacc. A); a second group was inoculated with a commercially available chemically inactivated feline panleukopenia viral vaccine (Vacc. C); and a third group with inactivated FPLV vaccine prepared in our laboratory by growing living attenuated FPLV (Leopard strain) (Vacc. L) in CCL 64 cells and by inactivating the virus with 0.25% formalin. According to the manufacturer, both commercial feline viral vaccines were produced by growing the FPV in cell cultures (tissue culture origin). The tissue cultures used for inactivated vaccine were treated with formaldehyde solution to insure viral inactivation. The vaccines were administered intramuscularly to dogs in doses of 1 cc. Neither the living nor inactivated FPLV vaccines caused any adverse effects in dogs during a 2-week period of observation prior to challenge-inoculation with virulent canine parvovirus. The vaccinated dogs in groups 1 and 2 and unvaccinated control dogs were challenge-inoculated 14 days after administration of one dose of FPLV living or inactivated vaccine. Dogs in group 3 were vaccinated twice, two weeks apart, and challenge-inoculated seven days after the last vaccination.